Pencil Tube Condenser Microphone

The M221B was a second-generation miniature tube microphone, and was one of the first to offer a series of interchangeable capsules for specific recording applications. It was a revision to the short-lived M221A, and differed primarily in the way capsules were attached to the microphone body:

• The M221A had female threads on the microphone body.
• The M221B and all subsequent versions had male threads on the microphone body.

The mic used a tube amplifier circuit based on the Telefunken AC701 subminiature triode.